# deduction guides for `std::array`

From cppreference.com
< cpp‎ | container‎ | array

Defined in header `<array>` |  |
template< class T, class... U > array( T, U... ) -> array<T, 1 + sizeof...(U)>; |  | (since C++17)

One deduction guide is provided for std::array to provide an equivalent of std::experimental::make_array for construction of `std::array` from a variadic parameter pack.

The program is ill-formed if (std::is_same_v<T, U> && ...) is not true. Note that (std::is_same_v<T, U> && ...) is true when sizeof...(U) is zero.

### Example

Run this code

    #include <algorithm>
    #include <array>
    #include <cassert>
    #include <type_traits>

    int main()
    {
        const int x = 10;
        std::array a{1, 2, 3, 5, x}; // OK, creates std::array<int, 5>
        assert(a.back() == x);

    //  std::array b{1, 2u}; // Error, all arguments must have the same type

    //  std::array<short> c{3, 2, 1}; // Error, wrong number of template args
        std::array c{std::to_array<short>({3, 2, 1})}; // C++20 facility
        assert(std::ranges::equal(c, std::array{3, 2, 1}));
        static_assert(std::is_same_v<short, decltype(c)::value_type>);
    }

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